Compositions For Liquid Crystal Display

ABSTRACT

This invention relates to compositions and an assembly process for the manufacture of liquid crystal displays. The assembly process is especially advantageous because it can be easily scalable to roll-to-roll continuous manufacturing of liquid crystal displays. The invention is directed to a photoalignable top-sealing composition for top-sealing a liquid crystal display cell.

This application is a divisional application of U.S. application Ser.No. 10/771,848, filed Feb. 4, 2004, which claims the benefit of U.S.Provisional Application No. 60/445,258, filed Feb. 4, 2003; bothapplications are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

This invention relates to novel compositions and an assembly process forthe manufacture of liquid crystal displays.

(b) Background

Liquid crystal displays (LCDs) have been the predominate display choicefor decades for many applications including watches, radios, PDAs,portable computers, tablet computers and projection TVs because of theirflatness, light weight, high definition, low driving voltages and lowpower consumption. However, even with many improvements in materials andassembly processes, large-size LCDs are still very difficult andtime-consuming to manufacture.

The basic components of a typical LCD consist of a thin layer of liquidcrystals, two plates each coated with an alignment layer and a pair ofpolarizers. In a typical LCD assembly process, the first step involvesthe preparation of the electrode plates. For active matrix colordisplays, the deposition and patterning of color filter elements areoften carried out on the top electrode plate and the formation of thinfilm transistors and metal interconnect lines is carried out on thebottom plate. For passive color displays, transparent electrodes arepatterned on both facing plates in perpendicular arrays and colorfilters on the viewing plate provide the full color display. After theelectrode plates are prepared, alignment layers are then coated on theelectrode plates and rubbed or buffed carefully to control theorientation and pretilt angle of the liquid crystals. The top and thebottom plates are then joined together using an edge seal adhesive withsmall hole(s) open for injection of a liquid crystal (LC) compositionby, for example, a vacuum filling process, into the gap between the twoplates. Spacers such as mono-dispersed particles, fibers or reliefpatterns prepared by lithography are used to precisely control the cellgap. Finally, the holes are filled with a sealant and the display cellis laminated with polarizer films and optionally a retardation film,compensation film or light management film, connected with drivercircuitry, and assembled with a backlight unit and a frame to completethe display assembly.

In the conventional LC injection process, the space created between thetwo plates is evacuated and the LC composition is introduced into thecell through the hole(s) left in the edge sealant. This step results insignificant waste of the LC composition and is typically a very slowprocess particularly for LCDs having a narrow cell gap. As the displaysize increases, the time required for the LC filling using theconventional process increases dramatically. The requirement of anarrower cell gap, in-plane switching (IPS) for a high speed or wideviewing angle renders the LC filling step even slower. For example, 4 to6 hours of the filling and sealing time is typically required for a 15″LCD and up to 20 hours has been reported for a 22″ LCD. Review of thetraditional LCD assembling processes can be found in “Liquid CrystalFlat Panel Displays: Manufacturing Sciences & Technology” by W. C.O'Mara (1993); “Flat Panel Display Handbook”, Display IndustryTechnology Review, 2nd ed., (2000) by Stanford Resource, Inc. and “FlatPanel Display 2002 Yearbook” by Nikkei Microdevices.

Filling the LC composition before assembling the two electrode plates(i.e., the “LC dropping method”) has been disclosed to shorten the LCfilling time [see S. Yanada etalin SID 01 Digest, pp. 1350 (2001); H.Kamiya et al, in SID 01 Digest, pp. 1354 (2001) and references citedtherein]. The LC dropping process includes (1) applying a UV edgesealant on an electrode plate, (2) dropping the liquid crystals onto thesurface, (3) assembling display cell by adhering a second substrateunder vacuum to the first electrode plate via the edge sealant, and (4)hardening the sealant by, for example, UV. The process reduces the LCfilling time and also reduces waste of the expensive LC material.However, the process is not straight-forward for the production of largedisplay panels. First of all, a vacuuming step is needed to assemble thedisplay cell. Secondly, a precise volume of the LC composition must bedripped onto the plate. Use of excess of the liquid crystal compositionmay result in defects or poor adhesion due to undesirable contaminationof the sealant by the LC composition. On the other hand, insufficientliquid crystal composition tends to result in undesirable air pocketstrapped in the display cell. As the panel becomes larger and the glasssubstrate becomes thinner, the electrode plate may be bended by vacuumand deviation of the LC volume in the cell may occur. This isparticularly true when soft or mobile spacers are used to define thecell gap. Thirdly, non-uniform hardening of the edge sealant may occurdue to the presence of opaque patterns in most TFT (thin filmtransistor) LCDs. Finally, this process is difficult to scale up toroll-to-roll manufacturing.

Roll-to-roll filling and sealing processes have been disclosed in acopending patent application Ser. No. 09/759,212 (corresponding to2002-0126249), for dispersed type LCDs. The content of this co-pendingapplication is incorporated herein by reference in its entirety.However, the two continuous filling/top-sealing processes disclosedtherein are not useful for most LCDs if an alignment layer is needed tocontrol the orientation and pretilt angle of the liquid crystals.

SUMMARY OF THE INVENTION

This invention is directed to novel compositions and an assembly processfor the manufacture of liquid crystal displays. The assembly process isespecially advantageous because it can be easily scalable toroll-to-roll continuous manufacturing of liquid crystal displays.

The first aspect of the invention is directed to a photoalignabletop-sealing composition for top-sealing a liquid crystal display cell.The photoalignable top-sealing composition may comprise a photoalignablepolymer, oligomer or a precursor thereof and a sealing solvent orsolvent mixture. The photoalignable top-sealing composition isimmiscible with the liquid crystal composition and has a specificgravity no greater than or preferably lower than that of the liquidcrystal composition.

The second aspect of the present invention is directed to a group ofnovel photoalignment polymers, oligomers and precursors thereof suitableto be used in a photoalignable top-sealing composition.

The third aspect of the invention is directed to processes fortop-sealing a liquid crystal display cell.

The fourth aspect of the invention is a novel assembly process forliquid crystal devices.

The fifth aspect of the invention is directed to a liquid crystaldisplay wherein the display cell is top-sealed by a photoalignabletop-sealing composition of the present invention, in particular aphotoalignable top-sealing composition comprising a novel photoalignablepolymer, oligomer or a precursor thereof of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a typical cross-section view of a liquid crystaldisplay prepared by the assembly process of the present invention. FIG.1B is the schematic drawing showing the three-dimensional view.

FIG. 2 illustrates several typical spacers built on the bottom substrateof the present invention.

FIG. 3A illustrates a typical LCD cell top-sealed by the traditionaledge-seal method. FIG. 3B shows a LCD cell top-sealed by a process ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

Unless defined otherwise in this specification, all technical terms areused herein according to their conventional definitions as they arecommonly used and understood by those of ordinary skill in the art.

For example, the term “alkyl” refers to an optionally unsaturated linearhydrocarbon radical of 1 to 30 carbon atoms, or an optionallyunsaturated branched or cyclic hydrocarbon radical of 3 to 30 carbonatoms. Exemplary alkyl groups are methyl, ethyl, cyclopropylmethyl,cyclohexyl, cyclohexylmethyl, octyl, n-decyl, ethenyl, 3-hexenyl, andthe like. The term “alkoxy” refers to the group —O—R^(a) wherein R^(a)is an alkyl as defined above. The term “aryl” refers to an organicradical derived from an aromatic hydrocarbon having 3 to 18 carbon atomsincluding, but not limited to, phenyl, naphthyl, anthracenyl and thelike. The term “alkylene” or “phenylene” refers to an alkyl or phenylmoiety respectively which may be substituted at two sites (e.g., twoends).

All publications, patent applications and patents cited in thisspecification are incorporated by reference in this application as ifeach individual publication, patent application or patent werespecifically and individually indicated to be incorporated by reference.

A typical LCD prepared according to the assembly process of the presentinvention is shown in FIG. 1A. The display typically has a top (i.e.,the second) substrate (11) and a bottom (i.e., the first) substrate(12). Each of the top (11) and the bottom (12) substrates may comprise aconductor layer or only one of the substrates comprises a conductorlayer.

On the bottom substrate (12), there are the first alignment layer (12 a)and optionally a conductor layer (12 b). The bottom substrate may notcomprise the first alignment layer (12 a); but this option is lesspreferred.

Spacers (13) and edge walls (13 a) are built by, for example, printing,coating or photolithography on the first alignment layer (12 a) tocontrol precisely the cell gap (i.e., the distance between the top andbottom substrates, or more precisely, the distance between the twoalignment layers, 12 a and 16). The spacers built on the first alignmentlayer (12 a) may be of any shape, preferably with a flat top surface.Some non-limiting examples of the spacers are shown in FIG. 2.

A liquid crystal composition (15) is filled into the top-opened displaycell(s) (14) which is/are top-sealed with a photoalignable sealing layer(16). The top substrate (11) which may comprise a transparent conductorlayer (not shown) is finally disposed on the top-sealed display cell(s),optionally with an adhesive layer or overcoat (17) which may itself be aphotoalignable layer or a pre-aligned layer. The top substrate (11) maybe disposed by a method such as lamination, coating, printing, vapordeposition, sputtering or a combination thereof onto the photoalignabletop-sealing layer (16) or onto the adhesive or overcoat layer (17). Thetop (11) or the bottom (12) substrate may have additional layers (notshown) such as a color filter, a moisture or oxygen barrier or anoptical compensation layer. Finally, polarizer film(s) (not shown)and/or other light management film(s) may be applied to the assembleddisplay panel.

It is understood that the present invention is applicable to all typesof LCDs. For example, it is applicable to both the passive and activeaddressing LCDs. For the passive LCD, the top and bottom electrodes arepatterned on the two substrates in a perpendicular manner. In an activeLCD, one of the substrates (11 and 12) may be a TFT (thin filmtransistor) backplane and the other substrate may be a non-patternedcommon conductor layer or an insulator layer (in-plane switching). Thesubstrate layers may be a polymeric film or sheet, glass, metal or metaloxide or the like.

I. Photoalicinable Top-Sealing Composition

In one embodiment, the photoalignable top-sealing composition maycomprise a photoalignable polymer, oligomer or a precursor thereofdissolved or dispersed in a sealing solvent or solvent mixture. Thephotoalignable top-sealing composition has a specific gravity no greaterthan, preferable less than, that of the LC composition and is immisciblewith the LC composition.

Suitable photoalignable polymers, oligomers and precursors thereof forthe top-sealing composition typically comprise a photoalignablefunctional group on the main chain or a side chain.

In one embodiment, the photoalignable top-sealing composition maycomprise a photoalignable polymer, oligomer or a precursor thereofcomprising a hydrocarbon repeating unit and a photoalignable functionalgroup on the main chain or a side chain.

In another embodiment, the photoalignable top-sealing composition maycomprise a photoalignable polymer, oligomer or a precursor thereofcomprising a siloxane repeating unit and a photoalignable functionalgroup on the main chain or a side chain.

In still another embodiment, the photoalignable top-sealing compositionmay comprise a photoalignable polymer, oligomer or a precursor thereofcomprising an acrylate, methacrylate or vinyl repeating unit and aphotoalignable functional group on the main chain or a side chain.

In still another embodiment, the photoalignable top-sealing compositionmay comprise a photoalignable condensation polymer or oligomercomprising a repeating unit such as a condensate of urethane, urea,carbonate, ester, amide, sulfone, imide, epoxide or formaldehyde and aphotoalignable functional group on the main chain or a side chain.

In a further embodiment, the photoalignable top-sealing composition maycomprise a random copolymer, a graft copolymer, a branch copolymer or ablock copolymer comprising a photoalignable group in the main chain or aside chain.

In yet a further embodiment, the photoalignable top-sealing compositionmay comprise a block copolymer with at least one photoalignable blockcomprising a photoalignable functional group on the main chain or a sidechain and another block(s) that is/are compatible with the sealingsolvent or other non-photoalignment polymer(s) such as binder(s) orthickener(s), if present, in the top-sealing composition.

In yet a further embodiment, the photoalignable top-sealing compositionmay comprise a graft copolymer with at least one photoalignable graftchain and a main chain that is compatible with the sealing solvent orother non-photoalignable polymers such as binder(s) or thickener(s), ifpresent, in the top-sealing composition.

In still another embodiment, the photoalignable top-sealing compositionmay comprise a precursor of the above-mentioned photoalignable polymersor oligomers and a photoalignable polymer or copolymer may be formedin-situ from the precursor before or during the hardening orphotoaligning of the top-sealing composition. The photoalignableprecursor may be dissolved or dispersed in a sealing solvent or solventmixture that is immiscible with the LC composition. Such usefulprecursors may include, but are not limited to, a copolymer ofisocyanatoethyl acrylate and a cinnamate compound end-capped with ahydroxyl or amino group. Alternatively, the photoalignable polymerprecursors may comprise (1) a diol or diamine having, for example, acinnamate group, and (2) their complementary multifunctional isocyanatesor epoxides which may react with (1) to form in-situ photoalignablepolymers or oligomers.

The functional group referred to above may be cinnamate, coumarin,chalcony, benzolidenenaphthalidine, benzaylideneacetophenone,diphenylacetylene, stilbazole, stilbene, diphenylacetylene, diazo,spiropyran or the like. It may also be a heteroderivative of afunctional group identified above. The term “heteroderivative” isunderstood throughout this application to include a functional group inwhich one or more carbon atoms is/are replaced with a heteroatom(s) suchas oxygen, nitrogen or sulfur.

In addition to the conditions that the photoalignment top-sealingcomposition must be immiscible with the liquid crystal composition andhas a specific gravity which is no greater than that of the liquidcrystal composition, the top-sealing composition must also haveacceptable tenting, wetting and adhesion properties.

Certain novel photoalignable polymers, oligomers or precursors thereofdisclosed in Section II below are particularly suitable for thephotoalignment top-sealing composition of the present invention.

Suitable sealing solvents may include, but are not limited to, straight,branched or cyclic C₁₋₁₂ hydrocarbons, C₁₋₄ alcohols, water and thelike, or mixtures thereof. Solvents with a low boiling temperature and alow specific gravity are particularly useful. Suitable hydrocarbonsolvents include, but are not limited to, hexane, cyclohexane, heptane,octane, nonane, decane, decalin and the like. Suitable alcohol solventsinclude, but are not limited to, methanol, ethanol, 1 -propanol,2-propanol,1 -butanol, 2-butanol, t-butanol and the like.

Typical concentration of the photoalignable polymer, oligomer or aprecursor thereof in the sealing solvent or solvent mixture is in therange of about 3 to about 25% by weight, preferably in the range ofabout 5 to about 15% by weight. The concentration may be varied toachieve optimal viscosity and surface tension of the sealingcomposition.

In one embodiment, the sealing composition may have a viscosity ofhigher than 50 cps, preferably between about 50 to about 10000 cps andmore preferably about 100 to about 5000 cps at room temperature.

A thickener may also be used to increase the viscosity, particularlywhen a low molecular weight photoalignable polymer, oligomer or aprecursor thereof is used. When the composition is dissolved ordispersed in a hydrocarbon solvent, suitable thickeners may include highmolecular weight binders such as polysiloxane, polyisoprene orpolybutadiene block copolymers (e.g., Kraton thermoplastic elastomersfrom Kraton Polymers, Houston, Tex.), poly(dodecyl acrylate)s orpoly(dodecyl methacrylate)s. When the composition is dissolved ordispersed in a lower alcohol, suitable thickeners may include polyvinylbutyrals and hydroxypropyl celluloses.

To increase the useful or addressable area of a LC display, it is highlydesirable to reduce the number of the spacers and the total areaoccupied by the spacers. However, as the total area or number of thespacers decreases, the degree of difficulty to top-seal the filled LCcell(s) increases. To achieve a satisfactory seamless top-sealing, it iscritical to have a sealing composition with good tenting properties tohold the top-sealing layer on the spacers and the edge walls throughoutthe entire assembling process.

In addition, the sealing layer must have a minimum thickness in order to“tent” over the supporting spacers and edge walls. The minimum thicknessfor optimal tenting may depend on the LC composition used. In oneembodiment, the thickness of the photoalignable top-sealing layer of thepresent invention may be in the range of about 1 to about 20 microns,preferably about 1 to about 8 microns and more preferably about 2 toabout 4 microns.

To improve the tenting properties, the top-sealing compositionpreferably also has good wetting properties over the edge walls andspacers. In one embodiment, a top-sealing composition having a surfacetension lower than that of the LC composition to be enclosed may be usedto improve the tenting properties. A surfactant may be used to reducethe surface tension. Useful surfactants include, but are not limited to,the FC surfactants from 3M Company, Zonyl fluorosurfactants from DuPont,fluoroacrylates, fluoromethacrylates, fluoro-substituted long chainalcohols, perfluoro-substituted long chain carboxylic acids orderivatives thereof and Silwet surfactants from OSi. Alternatively, alow surface tension solvent, such as hexane, heptane or Isopar, may beused to formulate the sealing composition.

Additional spacer particles or fibers, preferably those with very narrowsize distribution, may also be added into the photoalignable top-sealingcomposition to improve control of the cell gap and the tentingproperties.

The photoalignable top-sealing composition may further comprisenon-photoalignable polymer(s) and additive(s). Useful non-photoalignablepolymers for the top-sealing composition may be those mentioned above asbinders or thickeners. Useful additives for the photoalignabletop-sealing composition may include low molecular weight (less than1000) photoalignable dichroic compounds such as azobenzenes, stilbenesor spiropyrans.

II. Novel Photoalignable Polymers, Oligomers and Precursors Thereof

The following group of novel photoalignable polymers, oligomers orprecursors thereof are particularly suitable for the photoalignabletop-sealing composition of the present invention. The methods for theirsynthesis are also given.

wherein x is an integer of 1-5;

-   m and n are integers and their sum is ≧20, preferably ≧50,-   R₁, R₂, R₃, R₄ and R₅ are independently alkyl, aryl, alkylaryl or    their heteroatom derivatives thereof, preferably having 1-12 carbon    atoms, substituted or unsubstituted alkylsilyl derivatives; and-   R′ is a linking group such as alkylene, cycloalkylene or phenylene.

The term “heteroderivative” or “heteroatom derivative” is defined as aderivative of the alkyl, aryl or alkylaryl in which one or more carbonatoms is/are replaced with heteroatom(s) such as oxygen, nitrogen orsulfur.

Polysiloxanes of Formula (I) with a photoalignable group may besynthesized according to Reaction Scheme (I) shown below. To prepare thecopolymer of Formula (I) wherein R₁═R₆═Si(CH₃₎ ₃, R₂═R₃═R₄═CH₃, and R′=

cinnamic acid may first reacted with thionyl chloride to form thecorresponding acyl chloride which subsequently is reacted with3-cyclohexen-1-ol to form a vinyl containing cinnamate derivative.Hydrosilylation of the resultant cinnamate derivative withpoly(methylsiloxane) in the presence of Speier's catalyst results in apolysiloxane containing a photoalignable cinnamate side chain. Variouscopolymers of the polysiloxane of Formula (I) may also be synthesized tooptimize the glass transition temperature (Tg) of the polymer andcompatibility with solvents such as methanol, ethanol, isopropanol,hexane, cyclohexane, Isopars or other hydrocarbon solvents that areimmiscible with most liquid crystals. To further adjust the solubilityof the photoalignment polymer in the above-mentioned solvents and itsincompatibility with the liquid crystals, the substituents R₁, R₂, R₃,R₄ and R₅ and the linking group R′ may be independently fluorinated.

wherein n is integer ≧1, preferably ≧10 and more preferably ≧50; and thepolyol moiety may be formed from polyethylene glycol, polypropyleneglycol, poly tetramethylene glycol, polyester diol, polyalkylene diol ora fluorinated polyether diol.

Polyurethanes of Formula (II) with a photoalignable coumarin group onthe main chain may be synthesized according to Reaction Scheme (II)below. For example, 6,7-dihydroxycoumarin is first treated by ethylenecarbonate to afford a dihydroxyethoxy-functionalized coumarin which inturn is reacted with cyclohexane diisocyanate and a polyol to form apolyurethane of Formula (II).

wherein n is an integer ≧1, preferably ≧10 and more preferably ≧50; andthe polyol moiety may be formed from polyethylene glycol, polypropyleneglycol, poly tetramethylene glycol, polyester diol, polyalkylene diol ora fluorinated polyether diol.

Photoalignable polyurethanes of Formula (III) with cinnamate groups onthe main chain may be synthesized by Reaction Scheme (III) as shownbelow.

Alternatively, the diisocyanate and the diols containing photoalignablefunctional groups disclosed in Reaction Scheme (II) and (III) may beused directly in the sealing composition. In this case, a photoalignablepolymer will be formed in-situ during or after hardening of the sealinglayer.

Alcohol-soluble photoalignable copolymers of Formula (IV) may besynthesized from 7-hydroxycoumarin by procedures shown in ReactionScheme (IV) below. Suitable copolymers for the polymer modificationinclude, but are not limited to, acrylic acid copolymers, maleicanhydride copolymers such as vinylether-co-maleic anhydride,2-hydroxyethylacrylate copolymers and the like. Alternatively, hydroxylcoumarin or cinnamic acid may be reacted with glycidyl acrylate orglycidyl methacrylate, and subsequently copolymerized with vinylmonomers to obtain alcohol soluble photoalignable copolymers.

wherein x is an integer from 0 to 5;

-   m and n are integers and their sum is ≧30, preferably ≧100; and-   R is alkyl, aryl, alkylaryl, alkoxy, aryloxy, dialkylamino,    diarylamino or cyano, preferably having 1-12 carbon atoms.

Block copolymers of Formula (V) containing photoalignable groups mayalso be synthesized by, for example, block copolymerization ofp-(t-butyldimethylsiloxy)styrene or p-(t-BOC)styrene with a diene suchas butadiene, isoprene or 1,3-pentadiene followed by acid deprotectionto yield poly(hydroxystyrene-b-diene) which in turn is treated with acinnamoyl chloride derivative as shown in Reaction Scheme V below. Theresultant block polymer has a photoalignable block and a block that ishighly soluble in hydrocarbon solvents (such as hexane, cyclohexane,heptane or other Isopars). Upon coating onto a LC composition, thephotoalignable block tends to migrate to the interface with the LCcomposition to maximize the alignment efficiency.

Precursors of photoalignable polymers of Formula (VI) or (VII) such asdiepoxy-functionalized coumarin and diepoxy-functionalized cinnamatederivatives may be synthesized according to Reaction Schemes (VI) and(VII), respectively as shown below. Polyisocyanate or diisocyanatecarrying a cinnamate or coumarin group may also be synthesized byreacting the corresponding diol compound of Formula (VI) or (VII) with adiisocyanate such as toluene diisocyanate or isophorone diisocyanate.

III. Assembly Process of the Present Invention

Briefly, the assembly process comprises (a) adding and processing afirst alignment layer on a first substrate optionally comprising aconductive layer, (b) constructing edge walls on the first alignmentlayer by a method such as printing, coating or photolithography todefine the display periphery, (c) constructing or applying spacers onthe first alignment layer, (d) filling and top-sealing the displaycell(s) defined by the spacers and the edge walls with a photoalignabletop-sealing layer by a one-pass or two-pass top-sealing process, (e)hardening and photoalign the photoalignable layer, either simultaneouslyor sequentially, and finally (f) disposing a second substrate orelectrode layer over the top-sealed display cell(s) by a method such aslamination, coating, printing, vapor deposition, sputtering or acombination thereof, optionally with an adhesive or overcoat whichitself may be a photoalignable layer or a pre-aligned layer.

After the above steps are completed, polarizer(s) and other opticalfilms may be applied to the assembled display panel and driver circuitryis subsequently mounted. A backlight may also be installed fortransmissive or transflective devices. The assembly process of thisinvention may be carried out by a continuous conveyor or web process.The process not only dramatically improves the throughput and yield, butalso enables the formation of large-size liquid crystal displays in anefficient manner.

Details of the assembly process are given below.

(1) Construction of the Bottom Substrate (12)

Fabrication of the bottom or the first substrate (12) optionallycomprising a conductor layer may be accomplished by any of the methodsknown in the art, details of which can be found in “Liquid Crystal FlatPanel Displays” by William C. O'Mara, 1993.

The first alignment layer (12 a) may be deposited on the substrate (12).If a conductor layer (12 b) is present, the alignment layer (12 a) iscoated or deposited onto the conductor side (12 b) on the substrate. Thefirst alignment layer (12 a) may be the same as those typically used inLCD manufacturing such as a polyimide, a surfactant, a coupling agent ora photoalignment polymer or oligomer. After deposition and baking, thefirst alignment layer may be aligned by rubbing or exposure to apolarized light. In some applications, a diamond turn may be used tocreate microgrooves or grating structures for the LC alignment.

In general, the photoalignment polymers or oligomers may have aphotoalignment functional group on the main chain or a side chain. Theprecursors of the photoalignment polymers and copolymers having aphotoalignable functional group on the main chain or a side chain mayalso be useful. The functional groups may include, but are not limitedto, cinnamate, coumarin, chalcony, benzolidenenaphthalidine,benzaylideneacetophenone, diphenylacetylene, stilbazole, stilbene,diphenylacetylene, diazo, spiropyran and the like. While only certaingroups of photoalignment polymers or oligomers are specificallymentioned below, it is understood that all of the conventionalphotoalignable polymers may be used as the first alignment layer (12 a)on the bottom substrate in the assembly process of the presentinvention.

For example, photosensitive copolymers containing a cinnamate, coumarin,chalcony or diphenylacetylene group on the side-chain have been used asa photoalignment layer (see V. G. Chigrinov, et al, U.S. Pat. No.5,389,698; M. Schadt et al, J. SID 1997 5/4 367; Y. Makita et al, J.Photopoly. Sci. Technol. 1998,11,187; M. Obi et al, Chem. Mater.1999,11,1293-1301; O. Yaroshchuk, SID 00 Digest, pp-443-445; and J. Kimet al., SID 01 Digest, pp. 806-809) for liquid crystal devices. Thephotoalignment copolymers may be dissolved in, for example,N-methylpyrrolidone and applied to the substrate by roll transfercoating or spin coating.

Polymers with chromophores on the main chain (S Song et al, Jp. J. Appl.Phs. 1998, 37, 2620) and polyesters containing a phenylenediacryloylgroup on the main chain may also be used as a photoalignment layer.Polymethacrylates with a benzylidenephthalimide side chain may also beused as a photoalignment layer (“Polymethacrylate withBenzylidenephthal-imide Side-chains, Photocontrol of Alignment of aNematic Liquid Crystal”, Macromol. Chem. Phys. 1998, pp-199, 363-373 and375-383 by D. Suh) through polarized E/Z photoisomerization. Copolymersof styrene or polyphenylmaleimide containing ω-(4-chalconyloxy)alkylgroup on both the styrene units and phenylmaleimide units (see M. Kimuraet al., SID 01 Digest, pp.1162-1165 and SID 00 Digest, pp. 438-441; S.Nakata et al., SID 01 Digest, pp. 802-805) are also useful.

A group of linear and cyclic polymers or oligomers having aphotoreactive ethylene group used as an alignment layer are disclosed inU.S. Pat. No. 5,539,074. The monomer units of this group ofphotopolymers include acrylate, methacrylate, 2-chloroacrylate,2-phenylacrylate, acryloylphenylene, acrylamide, methacrylamide,2-chloroacrylamide, 2-phenylacrylamide, vinyl ether, styrenederivatives, vinyl ester, maleic acid derivatives, fumaric acidderivatives, siloxanes and epoxides. Acrylate, methacrylate,2-chloroacrylate, acrylamide, methacrylamide, 2-chloroacrylamide,styrene derivatives and siloxanes are the preferred monomers.

Another alternative is an azo or fluorinated azo dye film, particularlythe azo dye/polyimide mixture [see W. C. Yip et al, SID 01 Digest, pp1170-1173; and W. Gibbon, et al, Nature, London, 351, 49, (1991); V.Vorflusev, et al, Mol. Crysta.Liq. Cryst., 263, 577 (1995)].

In addition, the alignment layer (12 a) may also be formed from a novelphotoalignment polymer, oligomer or a precursor thereof as described inSection II above.

(2) Construction of Spacers

An edge wall (13 a) and spacers (13) may be deposited on the firstalignment layer (12 a) of the bottom substrate (12) by a method such asprinting, coating, embossing or photolithography. Photolithography usinga negatively working photoresist is preferred for the present inventionsince a highly smooth surface may be easily obtained. The spacers may beof any shape, preferably with a flat top surface as shown in FIG. 2.Additional spacer particles or fibers may be sprayed onto the alignedsubstrate. The height of the spacers and edge coating may be in therange of about 1 to about 20 um, preferably in the range of about 2 toabout 8 um. To improve the tenting properties of the subsequentphotoalignable top-sealing layer above the liquid crystal composition,edge walls and spacers with a flat top surface are preferred. Thediameter or width of the top surface of the spacers may be in the rangeof about 2 to about 30 microns, preferably in the range of about 5 toabout 15 microns. The thus prepared bottom substrate is referred tohereinafter as the “finished bottom substrate” or the “top-openeddisplay cell(s)” (14). It comprises a substrate, edge walls and spacersto define the active area and cell gap of the display. The finishedbottom substrate (14) may also comprise a conductor layer (12 b), thefirst alignment layer (12 a) or both. The first alignment layer (12 a),if present, may be aligned by rubbing before the edge walls or spacersare built on the substrate. When a photoalignable layer is used as thefirst alignment layer (12 a), photoalignment may be accomplished using apolarized (UV) light after the edge walls and spacers are constructed.If a conductor or electrode layer (12 b) is present, the first alignmentlayer (12 a), the edge walls (13 a) and spacers (13) are on the side ofthe conductor layer.

The edge walls (13 a) are needed to confine the liquid crystalcomposition within the active cell. The edge walls may be formed byprinting or coating a thermal or radiation curable material onto thefirst alignment layer of the first substrate. The spacers (13) not onlydefine the cell gap, but also serve as the support for thephotoalignable top-sealing layer to form a seamless seal above theliquid crystal composition. The edge walls and the spacers may be formedfrom conventional edge seal adhesives such as epoxy and silicone resinscommonly used in the LCD industry. Preferably, the edge walls andspacers are formed from UV curable resins including negatively workingphotoresists.

(3) Liquid Crystal Materials

Liquid crystal compositions (15) that may be used in the presentinvention are well known in the art. The novel assembly process issuitable for LCDs such as twisted-nematic (TN), super twisted nematic(STN), guest host, cholesteric, ferroelectric or dispersed types ofLCDs.

Examples of liquid crystal materials that may be used in the presentinvention include, but are not limited to, E7, TL205, TL213, BL006,BL009, BL037, ME5N.F, CCP-30CF3, PCH-3, CCP-3F.F.F, MLC mixture seriesfrom Merck KGaA (Darmstadt, Germany); 5HBF3, 5PCL, and 5HPFF from ChissoCorp. (Japan); and CCG-V-F, ME2N.F, and CPTP-3-2 from Dainippon Ink &Chemicals, Inc., (Japan). Review of liquid crystal materials may befound in W. C. O'Mara, “Liquid Crystal Flat Panel Displays” by VanNostrand Reinhold, (1993); T. J. Bunning, et al, ed., “Liquid Crystalsfor Advanced Technologies”, Materials Research Soc. Symp. Proceedings,Vol. 425 (2000); S. T. Wu and D. K. Yang, “Reflective Liquid CrystalDisplays”, John Wiley & Son, Ltd, (2001); N. March and M. Tosi, ed.,“Polymers, Liquid Crystals, and Low-Dimensional Solids”, Plenum Press(1984); G. W. Gray, and J. W. Goodby, “Smetic Liquid Crystals, Texturesand Structures”, Leonard Hill (1984); “P. Kirsch, et al, Mol. Cryst.Liq. Cryst., 346, 193 (2000) and Angew. Chem. Int. Ed., 39, 4216 (2000);T. Broschard, et al, IDW'00, paper FMC-3-1, Kobe, Japan (2000).

In guest-host systems, dichroic guest dyes including arylazo orpoly(arylazo) dyes may be used. Suitable dichroic dyes include Blue AB2,Red AR1 and Yellow AG1 from Funktionfluid Gmb (Germany) and SI-486(yellow), S1426 (red), M483 (blue), S344 (black), S428 (black) and S7(black) from Mitsui Toatsu. Nonionic azo and anthraquinone dyes may alsobe used in some cases. Examples include, but are not limited to, Oil RedEGN, Sudan Red, Sudan Blue, Oil Blue, Macrolex Blue, Solvent Blue 35,Pylam Spirit Black and Fast Spirit Black from Pylam Products Co.,Arizona, Sudan Black B from Aldrich, Thermoplastic Black X-70 from BASF,anthroquinone blue, anthroquinone yellow 114, anthroquinone red 111, 135and anthroquinone green 28 from Aldrich. In any case, the dyes must bechemically stable.

(4) Filling and Top-Sealing of Display Cell(s)

After the finished bottom substrate (14) which may also be called atop-opened display cell, is constructed, it is filled with a liquidcrystal composition (15) and top-sealed with a photoalignable sealinglayer (16) by either a one-pass or two-pass top-sealing process. Ineither case, the display cell is top-sealed before the top substrate(11) is joined onto the finished bottom substrate (14).

In the “one-pass filling and top-sealing method”, a photoalignablecomposition of the present invention is predispersed in a liquid crystalcomposition by, for example, an in-line blender, and immediately coatedonto the finished bottom substrate by Myrad bar, gravure, doctor blade,slot coating or slit coating. The photoalignable composition isimmiscible with the liquid crystal composition and has a specificgravity lower than that of the liquid crystal composition. Excess fluidmay be scraped away by a wiper blade or a similar device. Thephotoalignable top-sealing composition floats to the top and forms asupernatant layer above the liquid crystal layer.

Alternatively, the liquid crystal composition and the photoalignabletop-sealing composition of the present invention may be coatedsequentially onto the finished bottom substrate by a “two-pass” sealingprocess. In this method, the top-sealing of the cells may beaccomplished by first filling a liquid crystal composition into thetop-opened display cell defined by the finished bottom substrate (14),scraping away excess fluid by, for example, a rubber blade, and followedby overcoating a photoalignable top-sealing composition of the inventionover the liquid crystal layer. Interfacial polymerization orcrosslinking at the interface between the liquid crystals andphotoalignable layer may be beneficial to the sealing process.Intermixing between the liquid crystal composition and thephotoalignable overcoat can be significantly suppressed by the formationof a thin barrier layer at the interface by the interfacialpolymerization or crosslinking reaction. To further reduce the degree ofintermixing, it is highly desirable that the specific gravity of thephotoalignable top-sealing composition is no greater than that of theliquid crystals.

Volatile organic solvents as described above may be used to adjust theviscosity and specific gravity of the photoalignment composition, andthe dry thickness of the coating. When a volatile solvent is used in thephotoalignable top-sealing composition, it is also preferred that it isimmiscible with the liquid crystal composition and has a specificgravity no greater than that of the liquid crystal phase. The two-passovercoating process is particularly useful when the component(s) of theliquid crystal phase is at least partially soluble in the photoalignmentcomposition, or vice versa. To further reduce the degree of intermixingbetween the photoalignable layer and the liquid crystal phase, thefilled display bottom substrate may be chilled before the photoalignablecomposition is overcoated.

Solvents, thickeners or additives may also be used in the two-passprocess to optimize the rheology, wetting and tenting properties for thetwo-pass sealing method.

The hardening of the photoalignable top-sealing composition in eithermethod described above may be accomplished by heat, moisture, solventevaporation or exposure to radiation such as a polarized (UV) light. Thepolarized (UV) light may be used to simultaneously harden thephotoalignable top-sealing composition and align the liquid crystalsthrough the photoalignable layer. Alternatively the photoalignable layermay be hardened first by other means, and subsequently photoaligned byexposure to a polarized light. The top-sealing layer (16) formed byeither the one-pass or two-pass process not only seamlessly encloses theliquid crystal composition within the display cell(s), but also servesas the alignment layer for the liquid crystal composition.

A top substrate or electrode layer (11) is then disposed onto thetop-sealed and aligned liquid crystal cell by a method such aslamination, coating, printing, vapor deposition, sputtering or acombination thereof, to form the liquid crystal panel ready for moduleassembly. An additional layer (17) such as an adhesive, overcoat layeror color filter may be added between the top substrate or electrodeplate and the photoaligned sealing layer to improve the process latitudeor display performance. Alternatively the top substrate may be disposedonto the top-sealing layer first, and the latter is subsequentlyphotoaligned with a polarized (UV) light through one of thesubstrate(s). Optionally, the polarized light exposure may be carriedout under an electric field to further enhance the efficiency ofphotoalignment.

The top-sealing/photoalignment layer may have a thickness in the rangeof about 1 to about 20 microns, preferably from about 1 to about 8microns and more preferably from about 2 to about 4 microns.

Two schematic top-sealed LC cells of the present invention are shown inFIG. 3A and 3B. FIG. 3A illustrates a typical LCD cell edge-sealed by atraditional edge-sealing adhesive. In FIG. 3A, 31, 32, 32 a, 33 and 36are the second (top) substrate, the first (bottom) substrate, the firstalignment layer, the spacers or edge walls and the second alignmentlayer, respectively. The second substrate (31)/alignment layer (36)simply sits on the spacers and either no or negligible wetting curvaturemay be found between the spacers (33) and the alignment layer (36). FIG.3B shows a LCD cell top-sealed by a process of the present invention. InFIG. 3B, 31, 32, 32 a, 33 and 38 are the second (top) substrate, thefirst (bottom) substrate, the first alignment layer, the spacers or edgewalls and the second and top-sealing alignment layer, respectively. Inone embodiment, the top-sealing alignment layer (38) may be in contactwith the inside surface (33 a) of the spacers or edge walls (33). Inanother embodiment, as shown in FIG. 3B, there may be a wettingcurvature at the interface between the spacers or edge walls (33) andthe top-sealing photoalignment layer (38). Such a wetting curvature maybe beneficial for improved tenting and adhesion properties. However, thecurved portion should be kept small to achieve a wider viewing area (ora higher aperture ratio).

(5) Final Steps

The final steps of the novel assembly process are carried out by methodsknown in the art (see, for example, “Liquid Crystal Flat Panel Displays”by William C. O'mara, 1993).

One of the final steps of the assembly process for the liquid crystaldisplays is the application of the polarizer to the outside of eachsubstrate. Polarizer films are composite films which contain thepressure sensitive adhesive layer needed to attach the polarizer to theglass. The direction of polarization is selected for each side of theglass substrate. Usually, if the liquid crystal composition has a twistof a certain angle, then the polarizers will be set at this angle withrespect to one another. This allows light passing from one side androtated by the liquid crystals to pass through the other side, a“normal” white condition.

In some cases, a retarder or compensation film is applied prior to thepolarizer. Compensation films are useful for correction of a distinctyellow or blue color in STN displays. True black and white displays canbe obtained, and viewing angle is also increased using compensationfilms. Suitable film materials include polycarbonate and polymethylmethacrylate.

A completed display will ordinarily have driver integrated circuitsmounted on or near one of the glass substrates. The mounting isaccomplished by conventional means. Backlighting for the liquid crystaldisplays are also known in the art and is described in “Liquid CrystalFlat Panel Displays” by William C. O'mara, 1993.

It should be noted that the novel assembly process of the presentinvention can also be carried out in an automated manner continuously orsemi-continuously. A conveyor type of assembly process is particularlysuitable for LCD assembling.

While the present invention has been described with reference to thespecific embodiments thereof, it should be understood by those skilledin the art that various changes may be made and equivalents may besubstituted without departing from the true spirit and scope of theinvention. In addition, many modifications may be made to adapt aparticular situation, materials, compositions, processes, process stepor steps, to the objective, spirit and scope of the present invention.All such modifications are intended to be within the scope of the claimsappended hereto.

1. A photoalignable top-sealing composition for top-sealing and aligninga liquid crystal composition filled in a top-opened display cell, whichphotoalignable top-sealing composition is alignable by a polarizedlight.
 2. The composition of claim 1 which comprises a photoalignablepolymer, oligomer or a precursor thereof dissolved or dispersed in asealing solvent or solvent mixture.
 3. The composition of claim 2 whichhas a specific gravity no greater than that of the liquid crystalcomposition and is immiscible with the liquid crystal composition. 4.The composition of claim 2 wherein said photoalignable polymer, oligomeror a precursor thereof comprises a photoalignable functional group onthe main chain or a side chain.
 5. The composition of claim 2 whereinsaid photoalignable polymer, oligomer or a precursor thereof comprises ahydrocarbon repeating unit and a photoalignable functional group on themain chain or a side chain.
 6. The composition of claim 2 wherein saidphotoalignable polymer, oligomer or a precursor thereof comprises asiloxane repeating unit and a photoalignable functional group on themain chain or a side chain.
 7. The composition of claim 2 wherein saidphotoalignable polymer, oligomer or a precursor thereof comprises anacrylate, methacrylate or vinyl repeating unit and a photoalignablefunctional group on the main chain or a side chain.
 8. The compositionof claim 2 wherein said photoalignable polymer, oligomer or a precursorthereof comprises a repeating unit of a condensate of urethane, urea,carbonate, ester, amide, sulfone, imide, epoxide or formaldehyde and aphotoalignable functional group on the main chain or a side chain. 9.The composition of claim 1 which comprises a random copolymer, a graftcopolymer, a branch copolymer or a block copolymer having aphotoalignable functional group in the main chain or a side chain. 10.The composition of claim 1 which comprises a block copolymer with atleast one photoalignable block having a photoalignable functional groupon the main chain or a side chain and another block(s) that is/arecompatible with a sealing solvent or solvent mixture ornon-photoalignment polymers, if present, in the composition.
 11. Thecomposition of claim 1 which comprises a graft copolymer having at leastone photoalignable graft chain and a main chain that is compatible witha sealing solvent or solvent mixture or non-photoalignable polymers, ifpresent, in the composition.
 12. The composition of claim 1 whichcomprises a precursor of a photoalignable polymer or oligomer.
 13. Thecomposition of claim 4 wherein said photoalignable functional group isselected from the group consisting of cinnamate, coumarin, chalcony,benzolidenenaphthalidine, benzaylideneacetophenone, diphenylacetylene,stilbazole, stilbene, diphenylacetylene, diazo and spiropyran.
 14. Thecomposition of claim 2 wherein said photoalignable polymer, oligomer ora precursor thereof is selected from the group consisting of thefollowing:

wherein x is an integer of 1-5; m and n are integers and their sum is≧20, preferably ≧50, R₁, R₂, R₃, R₄ and R₅ are independently alkyl,aryl, alkylaryl or heteroatom derivatives thereof, substituted orunsubstituted alkylsilyl derivatives; and R′ is a linking group such asalkylene, cycloalkylene or phenylene;

wherein n is integer ≧1; and the polyol moiety is formed frompolyethylene glycol, polypropylene glycol, poly tetramethylene glycol,polyester diol, polyalkylene diol or a fluorinated polyether diol;

wherein n is an integer ≧1; and the polyol moiety is formed frompolyethylene glycol, polypropylene glycol, poly tetramethylene glycol,polyester diol, polyalkylene diol or a fluorinated polyether diol;

wherein x is an integer from 0 to 5; m and n are integers and their sumis ≧30; and R is alkyl, aryl, alkylaryl, alkoxy, aryloxy, dialkylamino,diarylamino or cyano;


15. The composition of claim 2 wherein said sealing solvent or solventmixture has a specific gravity no greater than the liquid crystalcomposition and is immiscible with the liquid crystal composition. 16.The composition of claim 15 wherein said sealing solvent or solventmixture is selected from the group consisting of straight, branched orcyclic C₁₋₁₂ hydrocarbons, C₁₋₄ alcohols, water and mixtures thereof.17. The composition of claim 16 wherein said hydrocarbon solvent isselected from the group consisting of hexane, cyclohexane, heptane,octane, nonane, decane and decalin.
 18. The composition of claim 16wherein said alcohol is methanol, ethanol, 1-propanol,2-propanol,1-butanol, 2-butanol or t-butanol.
 19. The composition ofclaim 2 wherein the concentration of said photoalignable polymer,oligomer or a precursor thereof in the sealing solvent or solventmixture is in the range of about 3 to about 25% by weight.
 20. Thecomposition of claim 19 wherein the concentration of said photoalignablepolymer, oligomer or a precursor thereof in the sealing solvent orsolvent mixture is in the range of about 5 to about 15% by weight. 21.The composition of claim 2 further comprising a non-photoalignablepolymer.
 22. The composition of claim 21 wherein said non-photoalignablepolymer is a polymeric binder or thickener.
 23. The composition of claim2 further comprising a low molecular weight photoalignable dichroiccompound.
 24. The composition of claim 23 wherein said photoalignabledichroic compound has a molecular weight of less than about
 1000. 25.The composition of claim 24 wherein said photoalignable dichroiccompound is selected from the group consisting of azobenzenes, stilbenesand spiropyrans.
 26. A photoalignable polymer, oligomer or a precursorthereof represented by one of the following formulas:

wherein x is an integer of 1-5; m and n are integers and their sum is≧20; R₁, R₂, R₃, R₄ and R₅ are independently alkyl, aryl, alkylaryl orheteroatom derivatives thereof, substituted or unsubstituted alkylsilylderivatives; and R′ is a linking group such as alkylene, cycloalkyleneor phenylene;

wherein n is integer ≧1; and the polyol moiety is formed frompolyethylene glycol, polypropylene glycol, poly tetramethylene glycol,polyester diol, polyalkylene diol or a fluorinated polyether diol;

wherein n is an integer ≧1; and the polyol moiety is formed frompolyethylene glycol, polypropylene glycol, poly tetramethylene glycol,polyester diol, polyalkylene diol or a fluorinated polyether diol;

wherein x is an integer from 0 to 5; m and n are integers and their sumis >30; and R is alkyl, aryl, alkylaryl, alkoxy, aryloxy, dialkylamino,diarylamino or cyano;


27. A liquid crystal display panel comprising display cells formed on abottom substrate, filled with a liquid crystal composition andtop-sealed by a photoalignable top-sealing layer before a top substrateis applied onto the display panel.
 28. The display panel of claim 27wherein said photoalignable top-sealing layer is formed from aphotoalignable top-sealing composition comprising a photoalignablepolymer, oligomer or a precursor thereof represented by one of thefollowing formulas:

wherein x is an integer of 1-5; m and n are integers and their sum is≧20; R₁, R₂, R₃, R₄ and R₅ are independently alkyl, aryl, alkylaryl orheteroatom derivatives thereof, substituted or unsubstituted alkylsilylderivatives; and R′ is a linking group such as alkylene, cycloalkyleneor phenylene;

wherein n is integer ≧1; and the polyol moiety is formed frompolyethylene glycol, polypropylene glycol, poly tetramethylene glycol,polyester diol, polyalkylene diol or a fluorinated polyether diol;

wherein n is an integer ≧1; and the polyol moiety is formed frompolyethylene glycol, polypropylene glycol, poly tetramethylene glycol,polyester diol, polyalkylene diol or a fluorinated polyether diol;

wherein x is an integer from 0 to 5; m and n are integers and their sumis ≧30; and R is alkyl, aryl, alkylaryl, alkoxy, aryloxy, dialkylamino,diarylamino or cyano;


29. The display panel of claim 27 wherein said photoalignabletop-sealing layer is formed from a photoalignable top-sealingcomposition comprising a photoalignable polymer, oligomer or a precursorthereof.
 30. The display panel of claim 29 wherein said photoalignablepolymer, oligomer or a precursor thereof comprises a photoalignablefunctional group selected from the group consisting of cinnamate,coumarin, chalcony, benzolidenenaphthalidine, benzaylideneacetophenone,diphenylacetylene, stilbazole, stilbene, diphenylacetylene, diazo andspiropyran.
 31. A liquid crystal display panel comprising display cellseach of said display cells comprises: a) spacers or edge walls; b) aliquid crystal composition filled therein, and c) a photoalignabletop-sealing layer which encloses the liquid crystal composition withineach cell.
 32. The liquid crystal display panel of claim 31 wherein saidphotoalignable top-sealing layer is in contact with the inside surfaceof the spacers or edge walls.
 33. The liquid crystal panel of claim 32wherein there is a wetting curvature at the interface between thespacers or edge walls and the photoalignable top-sealing layer.
 34. Theliquid crystal panel of claim 31 wherein said photoalignable top-sealinglayer has a thickness in the range of about 1 to about 20 microns. 35.The liquid crystal panel of claim 31 wherein said photoalignabletop-sealing layer has a thickness in the range of about 1 to about 8microns.
 36. The liquid crystal panel of claim 31 wherein saidphotoalignable top-sealing layer has a thickness in the range of about 2to about 4 microns.